Journal of the Society of Motion Picture Engineers (1930-1949)

SPLICING IN VIDEO RECORDING 243 down the picture is called a "field" and has a period, including the return time, of Vso of a second. The television system uses interlaced scanning in which only the alternate lines of the picture are scanned in one field, with the intervening lines scanned by the next field. Thus a television frame embraces two fields and has a period of Vso of a second. The lower figure shows the timing diagram of a motion picture camera, modified to fit video recording requirements. The time ti indicates the start of an exposure, this exposure continuing to ti. A second exposure starts at U and continues to U. The interval beteen t3 and U is l/u of a second as required by the motion picture system. The duration of each exposure is Vso of a second, allowing one full television frame to be recorded on each frame of film. \ \ \ \ \ \ \l \J \l 5T V \1 fa Ci, u CrtMtAT t* Fig. 1 — Timing diagram. The exposure timing mechanism constitutes the major difference in various video recording equipments now in service. In some cases an electronic timing circuit blanks the cathode-ray tube thus providing an electronic shutter. In others a mechanical shutter is used. Much of the following discussion will apply alike to both types of equipment. Where differences exist they will be pointed out. It is indicated in the figure that the interval available for film pulldown, t2 to £3> is Vwo of a second, which is 72 degrees of the camera cycle. The shortness of this interval made necessary the design oi special cameras for video recording. At present there are several 16-mm movements which meet this requirement and at least one 35-mm movement. Projecting certain points from the camera diagram to intercept the television diagram shows that the beginning and the end of an